U.S. patent application number 15/320773 was filed with the patent office on 2017-08-31 for apparatus for production of pulverulent poly(meth)acrylate.
This patent application is currently assigned to BASF SE. The applicant listed for this patent is BASF SE. Invention is credited to Robert Bayer, Andreas Daiss, Jurgen Freiberg, Marco Kruger, Karl J. Possemiers, Rudolf Schliwa.
Application Number | 20170246607 15/320773 |
Document ID | / |
Family ID | 50976541 |
Filed Date | 2017-08-31 |
United States Patent
Application |
20170246607 |
Kind Code |
A1 |
Daiss; Andreas ; et
al. |
August 31, 2017 |
Apparatus for Production of Pulverulent Poly(Meth)Acrylate
Abstract
An apparatus for production of pulverulent poly(meth)acrylate,
comprising a reactor or droplet polymerization, having an apparatus
for dropletization of a monomer solution for the production of the
poly(meth)acrylate, having holes through which the solution is
dropletized, an addition point for a gas above the apparatus for
dropletization, at least one gas withdrawal point on the periphery
of the reactor and a fluidized bed. The outermost holes through
which the solution is dropletized are positioned such that a
droplet falling vertically downward falls into the fluidized bed
and the hydraulic diameter at the level of the midpoint between the
apparatus for dropletization and the gas withdrawal point is at
least 10% greater than the hydraulic diameter of the fluidized
bed.
Inventors: |
Daiss; Andreas;
(Ludwigshafen, DE) ; Bayer; Robert; (Sinsheim,
DE) ; Schliwa; Rudolf; (Alzenau, DE) ;
Freiberg; Jurgen; (Lampertheim, DE) ; Possemiers;
Karl J.; ('S Gravenwezel, BE) ; Kruger; Marco;
(Mannheim, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BASF SE |
Ludwigshafen |
|
DE |
|
|
Assignee: |
BASF SE
Ludwigshafen
DE
|
Family ID: |
50976541 |
Appl. No.: |
15/320773 |
Filed: |
June 10, 2015 |
PCT Filed: |
June 10, 2015 |
PCT NO: |
PCT/EP2015/062895 |
371 Date: |
December 21, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J 2219/00247
20130101; B01J 4/001 20130101; C08F 2/01 20130101; B01J 2208/00893
20130101; B01J 8/24 20130101; C08F 120/14 20130101; B01J 8/1872
20130101 |
International
Class: |
B01J 8/18 20060101
B01J008/18; C08F 120/14 20060101 C08F120/14; B01J 8/24 20060101
B01J008/24 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 23, 2014 |
EP |
14173487.1 |
Claims
1. An apparatus for production of pulverulent poly(meth)acrylate,
comprising a reactor (1) for droplet polymerization, having an
apparatus for dropletization (5) of a monomer solution for the
production of the poly(meth)acrylate, having holes through which
the solution is dropletized, an addition point for a gas (13) above
the apparatus for dropletization (5), at least one gas withdrawal
point (19) on the periphery of the reactor (1) and a fluidized bed
(11), wherein the outermost holes through which the solution is
dropletized are positioned such that a droplet falling vertically
downward falls into the fluidized bed (11) and the hydraulic
diameter at the level of the midpoint between the apparatus for
dropletization (5) and the gas withdrawal point (19) is at least
10% greater than the hydraulic diameter of the fluidized bed (11),
wherein the reactor (1) widens conically above the fluidized bed
(11) to its maximum hydraulic diameter and the at least one gas
withdrawal point (19) is positioned at the transition from the
conical widening above the fluidized bed (11) to the cylindrical
wall of the reactor (1), wherein at the upper end of the widening
the diameter of the conical widening above the fluidized bed (11)
is greater than the diameter of the reactor wall above the conical
widening, wherein the reactor wall projects into the conical
widening so as to form an annular gap in which the gas withdrawal
point is positioned between the conical widening and the reactor
wall.
2. The apparatus according to claim 1, wherein the head (3) of the
reactor (1) takes the form of a frustocone and the apparatus for
dropletization (5) is positioned in the frustoconical head (3) of
the reactor (1).
3. The apparatus according to claim 1 or 2, wherein the ratio of
the area in the reactor (1) covered by the apparatus for
dropletization (5) relative to the area enclosed by a line
connecting the outermost holes is less than 50%.
4. The apparatus according to claim 1, wherein the apparatus for
dropletization (5) of the monomer solution has channels (25)
arranged in a star shape, with the holes formed at the base
thereof.
5. The apparatus according to claim 4, wherein at least the holes
at the edge of the channel (25) are formed in such a way that the
monomer solution exits from the holes at an angle relative to the
axis (29) of the reactor (1).
6. The apparatus according to claim 4, wherein the channel (25) is
connected at its base to at least one dropletizer plate in which
the holes for addition of the monomer solution are formed.
7. The apparatus according to claim 6, wherein the dropletizer
plates are angled along their longitudinal axis at the base
thereof.
8. The apparatus according to claim 6, wherein the holes of the
dropletizer plates along the longitudinal axis are lower in the
middle than at the edges.
9. The apparatus according to claim 6, wherein the holes of the
dropletizer plates are arranged in a plurality of rows of
holes.
10. The apparatus according to claim 1, wherein the holes in the
dropletizer plates have a diameter in the range from 25 to 500
.mu.m.
11. (canceled)
12. (canceled)
13. (Cancellled)
14. The apparatus according to claim 5, wherein the channel (25) is
connected at its base to at least one dropletizer plate in which
the holes for addition of the monomer solution are formed.
15. The apparatus according to claim 7, wherein the dropletizer
plates are angled along their longitudinal axis at the base
thereof.
16. The apparatus according to claim 7, wherein the holes of the
dropletizer plates are arranged in a plurality of rows of
holes.
17. The apparatus according to claim 8, wherein the holes of the
dropletizer plates are arranged in a plurality of rows of holes.
Description
[0001] The invention relates to an apparatus for production of
pulverulent poly(meth)acrylate, comprising a reactor for droplet
polymerization, having an apparatus for dropletization of a monomer
solution for the production of the poly(meth)acrylate, having holes
through which the solution is dropletized, an addition point for a
gas above the apparatus for dropletization, at least one gas
withdrawal point on the periphery of the reactor and a fluidized
bed.
[0002] Poly(meth)acrylates find use especially as water-absorbing
polymers which are used, for example, in the production of diapers,
tampons, sanitary napkins and other hygiene articles, or else as
water-retaining agents in market gardening.
[0003] The properties of the water-absorbing polymers can be
adjusted via the level of crosslinking. With increasing level of
crosslinking, there is a rise in gel strength and a fall in
absorption capacity. This means that centrifuge retention capacity
decreases with rising absorption under pressure, and the absorption
under pressure also decreases again at very high levels of
crosslinking.
[0004] To improve the performance properties, for example liquid
conductivity in the diaper and absorption under pressure,
water-absorbing polymer particles are generally postcrosslinked.
This only increases the level of crosslinking at the particle
surface, and in this way it is possible to at least partly decouple
absorption under pressure and centrifuge retention capacity. This
postcrosslinking can be performed in aqueous gel phase. In general,
however, ground and sieved polymer particles are surface coated
with a postcrosslinker, thermally postcrosslinked and dried.
Crosslinkers suitable for this purpose are compounds which comprise
at least two groups which can form covalent bonds with the
carboxylate groups of the hydrophilic polymer.
[0005] Different processes are known for production of the
water-absorbing polymer particles. For example, the monomers and
any additives used for production of poly(meth)acrylates can be
added to a mixing kneader, in which the monomers react to give the
polymer. Rotating shafts with kneading bars in the mixing kneader
break up the polymer formed into chunks. The polymer withdrawn from
the kneader is dried and ground and sent to further processing. In
an alternative variant, the monomer is introduced in the form of a
monomer solution which may also comprise further additives into a
reactor for droplet polymerization. On introduction of the monomer
solution into the reactor, it breaks down into droplets. The
mechanism of droplet formation may be turbulent or laminar jet
disintegration, or else dropletization. The mechanism of droplet
formation depends on the entry conditions and the physical
properties of the monomer solution. The droplets fall downward in
the reactor, in the course of which the monomer reacts to give the
polymer. In the lower region of the reactor is a fluidized bed into
which the polymer particles formed from the droplets by the
reaction fall. Further reaction then takes place in the fluidized
bed. Corresponding processes are described, for example, in WO-A
2006/079631, WO-A 2008/086976, WO-A 2007/031441, WO-A 2008/040715,
WO-A 2010/003855 and WO-A 2011/026876.
[0006] A disadvantage of all the processes that are conducted by
the principle of droplet polymerization, in which monomer solution
disintegrates into droplets and falls downward in a reactor to form
the polymer, is that droplets can coalesce on collision, and
droplets hitting the wall of the reactor can also stick and thus
lead to unwanted formation of deposits. Moreover, an increase in
the size of the fluidized bed is necessary in the case of scale-up
to the industrial scale, which leads to a significant increase in
energy consumption.
[0007] It is therefore an object of the present invention to
provide a reactor for droplet polymerization in which formation of
deposits as a result of droplets hitting the walls is minimized,
and in which, in addition, the energy requirement can be minimized
on the industrial scale.
[0008] The object is achieved by an apparatus for production of
pulverulent poly(meth)acrylate, comprising a reactor for droplet
polymerization, having an apparatus for dropletization of a monomer
solution for the production of the poly(meth)acrylate, having holes
through which the solution is dropletized, an addition point for a
gas above the apparatus for dropletization, at least one gas
withdrawal point on the periphery of the reactor and a fluidized
bed, wherein the outermost holes through which the solution is
dropletized are positioned such that a droplet falling vertically
downward falls into the fluidized bed and the hydraulic diameter at
the level of the midpoint between the apparatus for dropletization
and the gas withdrawal point is at least 10% greater than the
hydraulic diameter of the fluidized bed.
[0009] Through the configuration of the reactor for droplet
polymerization such that the hydraulic diameter at the level of the
midpoint between the apparatus for dropletization and the gas
withdrawal point is at least 10% greater than the hydraulic
diameter of the fluidized bed, it is ensured that only a small
portion of the droplets reaches the wall, and this only occurs
after a residence time at which the droplets are no longer tacky.
Furthermore, by virtue of the outermost holes through which the
solution is dropletized being positioned such that a droplet
falling vertically downward falls into the fluidized bed, droplets
are prevented from hitting the wall and adhering thereon, which
results in formation of a deposit.
[0010] The hydraulic diameter d.sub.h is calculated to be:
d.sub.h=4A/C
where A is the area and C is the circumference. By virtue of the
use of the hydraulic diameter, the configuration of the reactor is
independent of the shape of the cross-sectional area. This area
may, for example, be circular, rectangular, in the form of any
polygon, oval or elliptical. Preference is given, however, to a
circular cross-sectional area.
[0011] In order that the monomer solution leaving the apparatus for
dropletization is not sprayed onto the wall of the reactor, and in
order at the same time to configure the reactor advantageously both
in static terms and in terms of material expenditure, it is
preferable to form the head of the reactor in the shape of a
frustocone and to position the apparatus for dropletization in the
frustoconical head of the reactor.
[0012] The frustoconical configuration of the head of the reactor
can save material compared to a cylindrical configuration.
Moreover, a frustoconical head serves to improve the structural
stability of the reactor. A further advantage is that the gas which
is introduced at the head of the reactor has to be supplied through
a small cross section and subsequently flows downward in the
reactor without significant vortexing because of the frustoconical
configuration. The vortexing which can be established in the case
of a cylindrical configuration of the reactor in the head region
and a gas feed in the middle of the reactor has the disadvantage
that droplets that are entrained with the gas flow can be
transported against the wall of the reactor because of the
vortexing and hence can contribute to formation of deposits.
[0013] In order to keep the height of the reactor as low as
possible, it is also advantageous when the apparatus for
dropletization of the monomer solution is disposed as far upward as
possible in the frustoconical head. This means that the apparatus
for dropletization of the monomer solution is disposed at the level
in the frustoconical head at which the diameter of the
frustoconical head corresponds roughly to the diameter of the
apparatus for dropletization.
[0014] In order to prevent the monomer solution which leaves the
apparatus for dropletization in the region of the outermost holes
from being sprayed against the wall of the frustoconical head, it
is particularly preferable when the hydraulic diameter of the
frustoconical head, at the level at which the apparatus for
dropletization is disposed, is 2% to 30%, more preferably 4% to 25%
and especially 5% to 20% greater than the hydraulic diameter
corresponding to the area which is enclosed by a line connecting
the outermost holes. The somewhat greater hydraulic diameter of the
head additionally ensures that droplets, even below the reactor
head, do not prematurely hit the reactor wall and adhere
thereon.
[0015] In a further-preferred embodiment, the reactor widens
conically above the fluidized bed to its maximum hydraulic
diameter. The conical widening has the advantage that polymer
particles which have formed from the droplets through
polymerization of the monomer solution during their fall can fall
into the fluidized bed without being sucked out of the reactor
together with the offgas. Polymer particles which hit the conical
widening directly can slide into the fluidized bed with support by
suitable tappers on the outside of the conical part of the
reactor.
[0016] Through the addition point for gas above the apparatus for
dropletization of the monomer solution, gas and droplets flow
through the reactor from the top downward in cocurrent. Since the
fluidized bed is in the lower region of the reactor, the effect of
this is that gas flows from the bottom upward in the opposite
direction in the lower region of the reactor. Since gas is
introduced into the reactor at both from the top and from the
bottom, it is necessary to withdraw the gas between the apparatus
for dropletization of the monomer solution and the fluidized bed.
Preferably, the gas withdrawal point is positioned at the
transition from the conical widening above the fluidized bed to the
cylindrical wall of the reactor. The corresponding widening in the
cross section to the maximum reactor diameter at the level of the
gas withdrawal point prevents particle entrainment into the reactor
offgas. The cross-sectional area of the gas withdrawal ring is
sufficiently large that the mean gas velocity in the ring is 0.25
to 3 m/s, preferably 0.5 to 2.5 m/s and especially 1.0 to 1.8 m/s.
Smaller values do reduce particle entrainment, but lead to
uneconomically large dimensions; greater values lead to an
undesirably high particle entrainment.
[0017] The region of the reactor where the gas withdrawal point is
positioned is preferably configured such that the diameter of the
conical widening is greater at the upper end thereof than the
diameter of the upper section of the reactor. The gas flowing
through the reactor from the top flows around the lower end of the
reactor wall of the upper section and is withdrawn via at least one
gas draw point from the annular space formed between the upper end
of the conical widening and the lower end of the reactor wall that
projects into the conical widening. Connected to the gas draw point
is an apparatus for separation of solids, in which polymer
particles which are drawn off from the reactor with the gas flow
can be separated off. Suitable apparatuses for separating solids
are, for example, filters or centrifugal separators, for example
cyclones. Particular preference is given to cyclones.
[0018] According to the invention, the hydraulic diameter of the
fluidized bed is selected such that the area of the fluidized bed
is at least sufficiently large that a droplet falling vertically
downward from the outermost holes of the apparatus for
dropletization falls into the fluidized bed. For this purpose, the
area of the fluidized bed is at least just as large as and/or just
the same shape as the area which is formed by a line connecting the
outermost holes of the apparatus for dropletization. In addition,
it is also possible that the surface of the fluidized bed is larger
than the area which is formed by the line connecting the outermost
holes of the apparatus for dropletization. It is particularly
preferable when the surface area of the fluidized bed is 5% to 50%,
more preferably 10% to 40% and especially 15% to 35% greater than
the area formed by the line connecting the outermost holes of the
apparatus for dropletization. In this case, the shape of the
surface of the fluidized bed corresponds in each case to the shape
of the area which is enclosed by the line connecting the outermost
holes. If, for example, the surface of the fluidized bed is
circular, the area enclosed by the line connecting the outermost
holes is also circular, in which case the diameter of the surface
of the fluidized bed may be greater than the diameter of the area
which is formed by the line connecting the outermost holes of the
apparatus for dropletization.
[0019] Typically, the monomer solution exits from the holes of the
apparatus for dropletization in the form of a liquid jet which then
disintegrates into droplets in the reactor. The disintegration of
the liquid jet depends firstly on the amount of the liquid which
exits through the holes per unit time, and secondly on the velocity
and the volume of the gas flowing through the reactor. In addition,
the physical properties of the monomer solution and the geometry of
the holes affect the way in which the jet disintegrates. In the
context of present invention, droplet disintegration is also
referred to as dropletization.
[0020] In order that enough gas can flow past the apparatus for
dropletization of the monomer solution, so that a homogeneous gas
velocity in the reactor can be achieved and there is not excessive
acceleration and vortexing of the gas as it flows round the
apparatus, it is additionally preferable that the ratio of the area
covered by the apparatus for dropletization in the reactor relative
to the area which is enclosed by the line connecting the outermost
holes is less than 50% and is preferably in the range between 3%
and 30%.
[0021] It is additionally preferable when the number of holes
relative to the area which is formed by the line connecting the
outermost holes is in the range from 100 to 1000 holes/m.sup.2,
preferably in the range from 150 to 800 holes/m.sup.2 and
especially in the range from 200 to 500 holes/m.sup.2. This ensures
that the droplets formed at the holes have a sufficiently large
separation and can additionally come into sufficient contact with
the gas flowing through the reactor.
[0022] In one embodiment, the apparatus for dropletization of the
monomer solution comprises channels, with the holes formed at the
base thereof, and arranged in a star shape. The star-shaped
arrangement of the channels, especially in a reactor with circular
cross section, enables homogeneous distribution of the droplets in
the reactor. The addition is effected through the channels into
which the monomer solution is introduced. The liquid exits through
the holes at the base of the channels and forms the droplets.
[0023] In order that the droplets exiting from the channels come
into contact as quickly as possible with the gas flowing around the
channels, it is additionally preferable when the channels have a
minimum width. The width of the channels is preferably in the range
from 25 to 500 mm, further preferably in the range from 100 to 400
mm and especially in the range from 150 to 350 mm.
[0024] The number N.sub.RL of individual channels in the case of a
star-shaped arrangement is dependent on the circumference C of the
reactor at the position where the channels are arranged.
[0025] Preferably, the number of channels is within the range
defined below:
C 4.0 m .ltoreq. N RL .ltoreq. C 1.2 m ##EQU00001##
and especially
C 3.6 m .ltoreq. N RL .ltoreq. C 1.8 m ##EQU00002##
[0026] In these formulae, the circumference C should be used in
meters and "m" means meters. In addition to a configuration such
that the channels of the apparatus for dropletization are arranged
in a star shape, they may also be arranged in any desired
arrangement with respect to one another, for example parallel to
one another or overlapping one another, such that, for example, a
rectangular pitch or a triangular pitch is achieved by the
arrangement of the channels. In the case of a triangular pitch and
a rectangular pitch, a plurality of channels aligned in parallel
are aligned transverse to one another in each case, the angle
between the channels aligned transverse to one another being
90.degree. in the case of a rectangular pitch and preferably
60.degree. in the case of a triangular pitch.
[0027] It is additionally preferable when at least the holes at the
edge of the channel are formed in such a way that the monomer
solution exits from the holes at an angle relative to the axis of
the reactor. Through the exit of the monomer solution at an angle
relative to the axis of the reactor, it is possible to obtain a
more homogeneous distribution of the droplets in the reactor and a
greater separation of the droplets from a channel from one another.
In the case of a star-shaped arrangement of the channels, it is
additionally preferable when the angle at which the monomer
solution exits from the holes relative to the axis of the reactor
increases from the inside outward. The exiting of the liquid at an
angle relative to the axis of the reactor can be achieved either
through appropriate configuration of the holes, for example by
virtue of them being formed at an angle in the dropletizer plate,
or alternatively through angled configuration of the dropletizer
plate.
[0028] If the angle at which the droplets exit from the holes is
constant over the entire length of the individual channels of the
apparatus for dropletization, it is preferably in the range from 0
to 30.degree., preferably in the range from 0.1 to 20.degree. and
especially in the range from 0.2 to 15.degree..
[0029] Especially in the case of a star-shaped arrangement of the
channels, it is preferable when the angle at which the droplets
exit from the holes varies with the position of the hole, since the
distance between two channels increases from the middle outward.
Thus, it is advantageous when the angle closer to the middle is
smaller than the angle at the outer holes.
[0030] In the case of a star-shaped arrangement, it is preferable
when the angle .alpha. at which the liquid exits at least from the
holes at the radial edges is within the range defined below:
r N LR d P v 0.578 ( 0.00697 r + 0.0332 ) - 6.296 .ltoreq. .alpha.
.ltoreq. r N LR d P v 0.578 ( 0.00697 r + 0.0332 ) + 4.704 ,
##EQU00003##
preferably
r N LR d P v 0.578 ( 0.00697 r + 0.0332 ) - 4.296 .ltoreq. .alpha.
.ltoreq. r N LR d P v 0.578 ( 0.00697 r + 0.0332 ) + 2.704
##EQU00004##
and more preferably
r N LR d P v 0.578 ( 0.00697 r + 0.0332 ) - 2.296 .ltoreq. .alpha.
.ltoreq. r N LR d P v 0.578 ( 0.00697 r + 0.0332 ) + 1.704 ,
##EQU00005##
for the range of validity
0.25 m .ltoreq. r .ltoreq. 10 m ##EQU00006## 0.001 m .ltoreq. d P
.ltoreq. 0.0015 m ##EQU00006.2## 3 m s .ltoreq. v .ltoreq. 30 m s 3
.ltoreq. N LR .ltoreq. 18. ##EQU00006.3##
[0031] In these formulae, r is the radial position of the hole in
meters, N.sub.LR is the number of channels, d.sub.p is the mean
droplet diameter in meters and v is the droplet exit velocity in
meters per second. The angle a of the holes is found in degrees. If
a value less than zero is found, the value of 0.degree. should be
used for the angle in place of the value calculated.
[0032] The exit angle of the droplets relative to the axis of the
reactor can be optimized further by numerical simulation
calculations. As well as a constant change in the exit angle, it is
alternatively also possible to change the exit angle of the
droplets stepwise. For this purpose, in that case, the angle in the
middle of each stage is preferably fixed according to the above
definition.
[0033] For a simple revision of the apparatus for dropletization of
the monomer solution, it is additionally preferable when the
channel is connected at its base to at least one dropletizer plate
in which the holes for addition of the monomer solution are formed.
This firstly enables variation, for example, in the exit angle
and/or in the size of the holes through exchange of the dropletizer
plates in a simple manner as a function of the monomer solution or
of the desired droplet size; secondly, it is also possible to
exchange the dropletizer plates in a simple manner, in order, for
example, to clean used dropletizer plates when they are soiled.
[0034] Exiting of the liquid from the holes of the dropletizer
plates at an angle to the axis of the reactor can be achieved, for
example, by virtue of the dropletizer plates being angled along
their longitudinal axis at the base thereof. In the case of a
star-shaped arrangement of the channels and hence of the
dropletizer plates, the effect of this is that the liquid exits
from the holes at an angle relative to a plane running through the
axis of the reactor. The holes through which the monomer solution
is added to the reactor are preferably arranged in rows parallel to
the longitudinal axis of the dropletizer plate. The angle at which
the dropletizer plates are aligned relative to the horizontal
corresponds here to the exit angle of the droplets from the holes
to the vertical axis of the reactor. Especially in the case of use
of a plurality of dropletizer plates and a star-shaped arrangement
of the channels, it is advantageous when, in the event of variation
in the exit angle, each dropletizer plate in a channel has a
different angle which increases from the inside outward and is
determined in the middle of the dropletizer plate in each case by
the above definition.
[0035] As well as an angled configuration of the dropletizer
plates, any other configuration in which the holes of the
dropletizer plates along the longitudinal axis are lower in the
middle than at the edges is also possible. This is possible, for
example, when the dropletizer plate is formed in the form of a
circle segment along the longitudinal axis. It is also possible,
for example, to configure the dropletizer plates such that it has,
at the midpoint along the longitudinal axis, a region with a flat
profile, and the lateral regions to the left and right of the flat
region are angled toward the longitudinal axis or are configured in
the form of an arc.
[0036] In order to produce a sufficiently large number of droplets,
it is preferable when the holes in the dropletizer plates are
arranged in several rows of holes. It is especially preferable here
when the distance between the individual holes in a row of holes
and the distance between adjacent rows of holes are essentially the
same. A suitable distance between the holes in a row of holes and
of the rows of holes from one another is in the range from 1 to 100
mm, preferably in the range from 2 to 50 mm and especially in the
range from 3 to 20 mm.
[0037] In order to obtain droplets of a suitable size for
water-absorbing polymers, it is additionally preferable when the
holes in the dropletizer plates have a diameter in the range from
25 to 500 .mu.m.
[0038] Working examples of the invention are shown in the figures
and are more particularly described in the description which
follows.
[0039] The figures show:
[0040] FIG. 1 a longitudinal section through a reactor for droplet
polymerization,
[0041] FIG. 2 a longitudinal section through the reactor head,
[0042] FIG. 3 an arrangement of dropletizer channels in a first
embodiment,
[0043] FIG. 4 an arrangement of dropletizer channels in a second
embodiment,
[0044] FIG. 5 an arrangement of dropletizer channels in a third
embodiment,
[0045] FIG. 6 a cross section through a dropletizer channel in a
first embodiment,
[0046] FIG. 7 a cross section through a dropletizer channel in a
second embodiment,
[0047] FIG. 8 a cross section through a dropletizer channel in a
third embodiment.
[0048] FIG. 1 shows a longitudinal section through a reactor
configured in accordance with the invention.
[0049] A reactor 1 for droplet polymerization comprises a reactor
head 3 in which there is accommodated an apparatus for
dropletization 5, a middle region 7 in which the polymerization
reaction proceeds, and a lower region 9 having a fluidized bed 11
in which the reaction is concluded.
[0050] For performance of the polymerization reaction to prepare
the poly(meth)acrylate, the apparatus for dropletization 5 is
supplied with a monomer solution via a monomer feed 12. When the
apparatus for dropletization 5 has a plurality of channels, it is
preferable to supply each channel with the monomer solution via a
dedicated monomer feed 12. The monomer solution exits through
holes, which are not shown in FIG. 1, in the apparatus for
dropletization 5 and disintegrates into individual droplets which
fall downward within the reactor. Through a first addition point
for a gas 13 above the apparatus for dropletization 5, a gas, for
example nitrogen or air, is introduced into the reactor 1. This gas
flow supports the disintegration of the monomer solution exiting
from the holes of the apparatus for dropletization 5 into
individual droplets. In addition, the gas flow promotes lack of
contact of the individual droplets and coalescence thereof to
larger droplets.
[0051] In order firstly to make the cylindrical middle region 7 of
the reactor very short and additionally to avoid droplets hitting
the wall of the reactor 1, the reactor head 3 is preferably
conical, as shown here, in which case the apparatus for
dropletization 5 is within the conical reactor head 3 above the
cylindrical region. Alternatively, however, it is also possible to
make the reactor cylindrical in the reactor head 3 as well, with a
diameter as in the middle region 7. Preference is given, however,
to a conical configuration of the reactor head 3. The position of
the apparatus for dropletization 5 is selected such that there is
still a sufficiently large distance between the outermost holes
through which the monomer solution is supplied and the wall of the
reactor to prevent the droplets from hitting the wall. For this
purpose, the distance should at least be in the range from 50 to
1500 mm, preferably in the range from 100 to 1250 mm and especially
in the range from 200 to 750 mm. It will be appreciated that a
greater distance from the wall of the reactor is also possible.
This has the disadvantage, however, that a greater distance is
associated with poorer exploitation of the reactor cross
section.
[0052] The lower region 9 concludes with a fluidized bed 11, into
which the polymer particles formed from the monomer droplets fall
during the fall. In the fluidized bed, further reaction proceeds to
give the desired product. According to the invention, the outermost
holes through which the monomer solution is dropletized are
positioned such that a droplet falling vertically downward falls
into the fluidized bed 11. This can be achieved, for example, by
virtue of the hydraulic diameter of the fluidized bed being at
least as large as the hydraulic diameter of the area which is
enclosed by a line connecting the outermost holes in the apparatus
for dropletization 5, the cross-sectional area of the fluidized bed
and the area formed by the line connecting the outermost holes
having the same shape and the centers of the two areas being at the
same position in a vertical projection of one onto the other. The
outermost position of the outer holes relative to the position of
the fluidized bed 11 is shown in FIG. 1 with the aid of a dotted
line 15.
[0053] In order, in addition, to avoid droplets hitting the wall of
the reactor in the middle region 7 as well, the hydraulic diameter
at the level of the midpoint between the apparatus for
dropletization and the gas withdrawal point is at least 10% greater
than the hydraulic diameter of the fluidized bed.
[0054] The reactor 1 may have any desired cross-sectional shape.
However, the cross section of the reactor 1 is preferably circular.
In this case, the hydraulic diameter corresponds to the diameter of
the reactor 1.
[0055] Above the fluidized bed 11, the diameter of the reactor 1
increases in the embodiment shown here, such that the reactor 1
widens conically from the bottom upward in the lower region 9. This
has the advantage that polymer particles formed in the reactor 1
that hit the wall can slide downward into the fluidized bed 11
along the wall. To avoid caking, it is additionally possible to
provide tappers, not shown here, on the outside of the conical
section of the reactor, with which the wall of the reactor is set
in vibration, as a result of which adhering polymer particles are
detached and slide into the fluidized bed 11.
[0056] For gas supply for the operation of the fluidized bed 11, a
gas distributor 17 present beneath the fluidized bed 11 blows the
gas into the fluidized bed 11.
[0057] Since gas is introduced into the reactor 1 both from the top
and from the bottom, it is necessary to withdraw gas from the
reactor 1 at a suitable position. For this purpose, at least one
gas withdrawal point 19 is disposed at the transition from the
middle region 7 having constant cross section to the lower region 9
which widens conically from the bottom upward. In this case, the
wall of the cylindrical middle region 7 projects into the lower
region 9 which widens conically in the upward direction, the
diameter of the conical lower region 9 at this position being
greater than the diameter of the middle region 7. In this way, an
annular chamber 21 which surrounds the wall of the middle region 7
is formed, into which the gas flows and can be drawn off through
the at least one gas withdrawal point 19 connected to the annular
chamber 21.
[0058] The further-reacted polymer particles of the fluidized bed
11 are withdrawn by a product withdrawal point 23 in the region of
the fluidized bed.
[0059] FIG. 2 shows a longitudinal section through the reactor
head.
[0060] In the embodiment shown here, the reactor head 3 is conical.
The apparatus for dropletization 5 comprises individual channels 25
which project into the reactor 3 in a star shape from the outside
to the middle of the reactor head 3. In order to promote lack of
impact of the droplets leaving the apparatus for dropletization 5
with the wall of the reactor 1, the channels in the embodiment
shown here are arranged in the reactor head 3 at an angle 13 to the
horizontal. The angle .beta. is preferably in the range from
0.degree. to 20.degree., more preferably in the range from
0.degree. to 15.degree., especially preferably in the range from
0.degree. to 10.degree. and especially in the range from 0.degree.
to 5.degree.. By virtue of the corresponding alignment of the
channels, the droplets exit from the channels at an angle pointing
toward the middle of the reactor, such that the risk of droplets
being able to arrive at the wall of the reactor 1 and cake thereon
is minimized further.
[0061] A corresponding star-shaped arrangement of the channels 25
is shown in FIG. 3. Further possible arrangements of the channels
are shown in FIGS. 4 and 5. In these, however, an arrangement with
an angle .beta. to the horizontal can be achieved only with
difficulty, such that the channels 25 in this case preferably run
horizontally. FIG. 4 shows an arrangement in rectangular pitch, in
which the individual channels 25 each arranged at an angle of
90.degree. to one another, such that the points of intersection 27
of the channels each form rectangles, preferably squares.
[0062] FIG. 5 shows an arrangement in triangular pitch. The
channels 25 here are each arranged at an angle of 60.degree.
relative to one another, such that the points of intersection 27 of
the channels 25 each form equilateral triangles. However, this
additionally requires the channels that run parallel in each case
always to have an equal separation.
[0063] As an alternative to the embodiments shown here, it is of
course also possible to arrange the channels such that the distance
between channels arranged in parallel varies, or the distance
between the channels arranged in parallel is equal in each case but
the distances between the channels that are arranged in parallel
and run in different directions are different. In addition, it is
also possible to arrange the channels at any other angle relative
to one another.
[0064] Especially in the case of a circular reactor cross section,
however, the star-shaped arrangement shown in FIG. 3 is preferred.
In this case, however, the number of channels may vary as a
function of the circumference of the reactor. In addition, it is
possible to configure the channels with different lengths, such
that they project into the reactor 1 to different extents. However,
a rotationally symmetrical arrangement is always preferred.
[0065] The position of dropletizer plates 26 which conclude the
channels for supply of the monomer solution at the base thereof,
and in which the holes through which the monomer solution is
dropletized into the reactor are formed, is shown in FIGS. 3 to 5
by the dotted areas.
[0066] FIGS. 6, 7 and 8 show cross sections through the channels 25
in different embodiments.
[0067] In order to obtain a homogeneous droplet distribution over
the reactor cross section, it is preferable when at least the
droplets that are formed in a channel in the outer holes exit at an
angle to the vertical, i.e. to the reactor axis. For this purpose,
it is possible, for example, to configure the region of the channel
in which the holes are formed, as shown in FIG. 6, in the form of a
circle segment. As a result of this, the angle a at which the
monomer solution exits in relation to the reactor axis 29 increases
from the middle of the channel outward.
[0068] Alternatively, it is also possible, as shown in FIG. 7, to
align the channel base in which the holes are formed at an angle to
the horizontal, in which case, for holes at right angles to the
channel base 31, the angle a at which the droplets exit relative to
the reactor axis corresponds to the angle a of the channel base to
the horizontal. Another possibility is a configuration in which, in
addition to the angled regions of the channel base 31, a middle
base region 33 runs horizontally.
[0069] In order to enable simple cleaning of the holes, it is
advantageous when the holes are formed in dropletizer plates which
are positioned at correspondingly configured orifices in the base
of the channels 25. The dropletizer plates can then be deinstalled
for cleaning and replaced by clean dropletizer plates. In this
case, the dropletizer plates are preferably configured either in
the form of a circle segment or in angled form, in order that a
base profile of the channel 25 as shown in FIGS. 6 to 8 can be
achieved.
[0070] Especially in the case of a star-shaped arrangement of the
channels, it is additionally preferable when the angle at which the
monomer solution exits increases from the middle of the reactor
outward.
[0071] As well as the circular cross section shown here, it is also
possible to configure the channels 25 with any other cross section.
Especially when dropletizer plates are used, it is particularly
preferable to form the channels 25 with a rectangular cross
section. In this case, the channel may be sealed at the top by a
removable lid, and the dropletizer plates may be removed and
exchanged in a simple manner after removal of the lid.
LIST OF REFERENCE NUMERALS
[0072] 1 reactor [0073] 3 reactor head [0074] 5 apparatus for
dropletization [0075] 7 middle region [0076] 9 lower region [0077]
11 fluidized bed [0078] 12 monomer feed [0079] 13 addition point
for gas [0080] 15 position of the outermost holes in relation to
the fluidized bed 11 [0081] 17 gas distributor [0082] 19 gas
withdrawal point [0083] 21 annular chamber [0084] 23 product
withdrawal point [0085] 25 channel [0086] 26 dropletizer plate
[0087] 27 point of intersection [0088] 29 reactor axis [0089] 31
channel base [0090] 33 middle region of base
* * * * *